The present invention relates to a PTO transmission system in an agricultural or industrial vehicle, that is, a work vehicle, for transmitting power to a PTO shaft driving an implement, said vehicle comprising an engine and ground drive wheels driven by main or traction drive transmission means comprising a continuously variable transmission (CVT) or a power shift transmission, wherein the PTO transmission system comprises a planetary drive unit having first and second input means and output means, said first input means being adapted to be coupled to an output shaft of said engine, said second input means being adapted to be coupled to an output shaft of drive motor means and said output means being adapted to be coupled to said PTO shaft, said output means having a rotational speed which is a function of a rotational speed of the first and second input means; power source means; and control means adapted to control the transfer of power from said power source means to said drive motor means and coupled to sensor means adapted to sense the vehicle wheel speed and the PTO shaft speed.
Present day agricultural or industrial vehicles and specifically tractors comprise electronic engine controls and continuously variable transmissions (CVT) or power shift transmissions in an effort to provide optimum performance and fuel efficiency.
On the other hand, most PTO driven implements require a constant drive shaft speed or a drive shaft speed governed by other considerations to insure proper operation.
Therefore, PTO transmission systems for agricultural or industrial vehicles for transmitting power to a PTO shaft driving an implement or variable transmissions between the PTO shaft and drive means on the implement itself have been designed in an effort to allow the control the working speed of such implements independent from the wheel speed of the vehicle or the speed of rotation of the engine thereof.
Examples for such PTO transmission systems may be found in the U.S. Pat. No. 6,692,395 or the DE-A1-196 21 391. These PTO transmission systems use planetary gear units having two input shafts driven by the engine and an auxiliary drive motor, and an output shaft for driving the PTO shaft. By changing the speed of rotation of the auxiliary drive motor, the speed of the PTO shaft may be varied in relation to the engine speed. The energy consumption of such auxiliary drives is relatively high and it still is not possible to readily adapt the PTO transmission system to different implements and working conditions.
The present invention is directed to a PTO transmission system and a method of operating thereof, wherein the power consumption is reduced and which is readily adaptable to different implements and working conditions.